These calendar commands display the dates and times of the phases of
the moon (new moon, first quarter, full moon, last quarter). This
feature is useful for debugging problems that "depend on the phase of
the moon."

M

Display the dates and times for all the quarters of the moon for the
three-month period shown (calendar-phases-of-moon).

M-x phases-of-moon

Display dates and times of the quarters of the moon for three months around
today's date.

Within the calendar, use the M command to display a separate
buffer of the phases of the moon for the current three-month range. The
dates and times listed are accurate to within a few minutes.

Outside the calendar, use the command M-x phases-of-moon to
display the list of the phases of the moon for the current month and the
preceding and succeeding months. For information about a different
month, use C-u M-x phases-of-moon, which prompts for the month and
year.

The dates and times given for the phases of the moon are given in
local time (corrected for daylight savings, when appropriate); but if
the variable calendar-time-zone is void, Coordinated Universal
Time (the Greenwich time zone) is used. Section 31.12.